Maintaining a well-structured software system

It has been theorized that if a software system is developed using a rigorous methodology and is well documented and well structured, the resulting system will be more easily maintained. The author describes experiences with a large, real-time software system that successfully uses structured techniques, including an iterative life cycle during maintenance. The following advantages are found: (1) the completely documented, modular design makes it possible to estimate accurately the cost of enhancements, both in terms of manpower and schedule; (2) the existence of thorough and accurate user documentation permits the results of requirements analysis to be presented to the user in very specific terms, thereby increasing the opportunities for feedback; (3) the structured, documented design allows the system to be maintained by a less experienced staff, which reduces both cost and risk of attrition; and (4) the easily understood, structured code reduces the probability that minor functional enhancements will be difficult to install or will have an undesirable systemwide impact.<>